Hard body armour typically incorporates an ultra-hard, ballistic ceramic top layer combined with a laminated blend of unidirectional-oriented fiber bundles which work together to stop bullets and fragments. Depending on the level of threat (i.e. 9 mm 124 grain or 7.62 mm/M80 NATO 147 grain.), hard armour works by disrupting the aerodynamic shape of the bullet and dissipating the energy through the shattering of the ceramic top layer. The blunted or shattered bullet and the ceramic fragments (secondary projectile) are caught in the laminated blend of high performance fibers, thereby inhibiting penetration.
In Canada and the United States, body armour levels are certified by the National Institute of Justice (NIJ). The levels are I, IIA, II, IIIA, III, and IV. Based on extensive laboratory tests, researchers classify any new body armour design into one of the six levels: Level I body armour offers the lowest level of protection and level IV offers the highest. The body armour classes are often described by what sort of weaponry they guard against. The lowest level body armour can only be relied on to protect against bullets with relatively low energy, which tend to have less force on impact. Some higher-level body armour can protect against higher energy bullets (i.e. 44 magnum and 357 magnum). Categories I through IIIA are soft, concealable, and primarily made with Kevlar or other ballistic materials. Type III and Type IV use hard rigid plates made from ceramics, to defeat high energy rifle rounds.
There are two different types of body armour currently on the market and used by law enforcement and the military:
Soft body armour—Soft body armour made with panels of flexible ballistic fabric, such as Kevlar (Trade Mark of Duport). Kevlar-brand fiber works by “catching” a bullet in a multilayer web of woven fabrics. The engaged fibers absorb and disperse the energy of the impact to other fibers in the fabric weave. This transfer of energy occurs at “crossover points” where the fibers are interwoven. Additional energy is absorbed by the other layers in the body armour reducing the amount of transferred energy that causes “blunt trauma.” These woven fabrics are strong enough to perform, while offering the additional advantage of being more comfortable to wear than traditional plastic-based (polythylene) shield products. Another soft armour material is Spectra Shield (Trade Mark of Honeywell), it is not a woven material, but instead a thin, flexible ballistic composite made from two layers of unidirectional fibers held in place by flexible resins. These Spectra fibers are arranged so they cross each other at 0 and 90 degree angles. Then, both fiber and resin layers are sealed between two thin sheets of polythylene film.
Current weaknesses of soft body armour are:
Type of stopping power is determined by the number of layers; the higher the caliber of bullet the more layers of ballistic fabric are needed. As layers increase in number they become bulkier, less flexible, and heavier. This creates a disadvantage for the wearer. Without any hard armour (i.e. Ceramic plate) ballistic fabric is incapable of stopping high powered weapons.
If ballistic fabric is subjected to high humidity or any type of liquid the soft armour can lose its integrity. If the soft armour becomes wet, the water acts as a lubricant and allows the projectile to slip between the weaves of the material, thereby injuring the wearer.
Soft-body armour is incapable of stopping sharp-edged objects. Due to the    a. design of ballistic fabric, sharp objects can cut through and penetrate the armour.
4. Ballistic fabric is not recyclable. As each new generation of Kevlar is created, previous generations become obsolete and undesirable for use.
Hard-body armour—Hard-body armour is made out of thick ceramic or metal plates; it functions basically the same way as the iron suits worn by medieval knights: It is hard enough that a bullet or other weapon is deflected. That is, the armour material pushes out on the bullet with the same force (or nearly the same force) which the bullet pushes in, so the armour is not penetrated.
Current weaknesses of hard body armour/protective ceramic plates are:
They are not flexible and deflect energy more than absorb it. This results in the material needing to be very hard.
They are heavy and cumbersome.
Once compromised, the plates must be replaced and new ones purchased resulting in high replacement costs. A single shot can cause this problem and continuous shots can guarantee the plate's failure.
Ceramic plates must be handled with care. If handled carelessly, the plates can crack or chip, rendering the plate ineffective.
Plates must always be inspected after use. This is an expensive and complicated procedure.
Although ceramic plates are effective against most calibers, when the plates are subjected to high caliber rounds (i.e. 7.62×51 mm Ruag AP (Armour Piercing) rounds)) they are compromised and their reliability is unpredictable.
Ceramic plates are not recyclable. Once they are compromised, the plates must be discarded.
These two different types of body armour can be combined to create a stronger type of armour capable of stopping some high-powered rifle rounds depending on the threat level of the armour.
Weaknesses of this combined armour:
Combinations result in heavy and cumbersome plate systems that are uncomfortable for the wearer.
Once the hard armour is compromised the soft armour is ineffective against most ballistic rounds.
If the ceramic plates are broken, the shrapnel of the plates can penetrate the soft armour causing injury of the wearer.
Vehicle Armour
Current Versions of Vehicle Armour
Spaced Armour
Armour with two or more plates spaced a distance apart, called spaced armour, when sloped reduces the penetrating power of bullets and solid shot as after penetrating each plate they tend to tumble, deflect, deform, or disintegrate. When not sloped, they reduce the protection offered by the armour, and detonate explosive projectiles before they reach the inner plates.
Spaced armour protects against high explosive anti-tank (HEAT) projectiles which create a focused jet of plasticized metal, very effective at the focus point, but not around this point. Relatively thin armour plates or even metal mesh can be attached as side skirts or turret skirts on tanks and other armoured vehicles. This light armour detonates the warhead prematurely so that the jet of molten metal is focused well before the main armour, becoming relatively ineffective.
In response to increasingly effective HEAT warheads, integral spaced armour was introduced. This type of armour possesses hollow spaces, increasing the length of travel from the exterior of the vehicle to the interior for a given weight of armour, to reduce the shaped charge's penetrating power. Sometimes the interior surfaces of these hollow cavities are sloped, presenting angles to the anticipated path of the shaped charge's jet in order to further dissipate its power. For example, a given weight of armour can be distributed in 2 layers 15 cm (6 in) thick instead of a single 30 cm (12 in) layer, giving much better protection against shaped charges.
Today light armoured vehicles mount panels of metal mesh, known as “slat armour”, and some main battle tanks carry rubber skirts to protect their relatively fragile suspension and front belly armour.
Composite Armour
Composite armour is armour consisting of layers of two or more materials with significantly different chemical properties; steel and ceramics are the most common types of material in composite armour. Composite armour's effectiveness depends on its composition and may be effective against kinetic energy penetrators as well as shaped charge munitions; heavy metals are sometimes included specifically for protection from kinetic energy penetrators. Composite armour can be highly effective but tends to be cumbersome and heavy as threat levels increase.
Reactive Armour
Explosive reactive armour uses layers of high explosive sandwiched between steel plates. When a shaped-charge warhead hits, the explosive detonates and pushes the steel plates into the warhead, disrupting the flow of the charge's liquid metal penetrator (usually copper at around 500 degrees; it can be made to flow like water by sufficient pressure). It is less effective against kinetic penetrators. Reactive armour poses a threat to friendly troops near the vehicle. Non-explosive reactive armour is an advanced spaced armour which uses materials which change their geometry so as to increase protection under the stress of impact.
Active protection systems use a sensor to detect an incoming projectile and explosively launch a counter-projectile into its path.
Electrically Charmed Armour
Electrically charged armour is a recent development in the UK by the Defense Science and Technology Laboratory. A vehicle is fitted with two thin shells, separated by insulating material. The outer shell holds an enormous electrical charge, while the inner shell is a ground. If an incoming HEAT jet penetrates the outer shell and forms a bridge between the shells, the electrical energy discharges through the jet, disrupting it. Trials have so far been extremely promising, and it is hoped that improved systems could protect against KE penetrators. Developers of the Future Rapid Effect System (FRES) series of armoured vehicles are considering this technology.
Technologies
For greater efficiency, the heaviest armour plates are placed on the front of APVs (Armoured Personnel Vehicles): on the gun mount. Sloping and curving armour both increase its protection. This is due to the fact that the given fixed thickness of armour plate (usually between 10″ to 12″), a projectile striking at an angle must penetrate more armour than one impacting perpendicularly. An angled surface also increases the chance of deflecting a projectile. Many APVs have “spall liners” inside of the armour, designed to protect the crew and equipment inside from fragmentation (spallation) released from the impact of enemy shells. Spall liners are made of Kevlar or similar materials.
Current Weaknesses of Vehicle Armour
Current vehicles use thick plates of various metals to protect the personnel inside. These plates are very heavy, cumbersome, and reduce the space inside for the crew.
Due to their mass, the plates can hinder the movement of the vehicle and in some cases must be removed in order for the vehicle to maintain a satisfactory level of maneuverability.
If plates are removed, the vehicle then becomes highly vulnerable to weapons attack, usually in the form of IEDs (Improvised Explosive Devices). IEDs have been known to penetrate the interior of AFVs killing or wounding the vehicle's crew and immobilizing it.
Current weapons such as the AK-47 rifles can fire the 7.62×39 armour piercing round which can penetrate the 10″-12″ armour plates on most APVs.